2020.12 = New features so awesome, we skipped a few numbers!
2020.8.2 = Oh sh*t!! Pull it back!!
2020.x is the year.
x.8.x or x.12.x is week 8 or week 12 (or whatever week of the year the base release was finalized)
x.x.1 or x.x.2 are bug fix patches on top of existing releases.... (and why I don't recommend setting updates to advanced... it's pretty rare the first release of anything doesn't have issues so you often want to wait for the .1 or .2 release to actually update.)